1. Field of the Invention
The present invention relates to an actuator used for driving an optical pick-up device writing or reading data on or from an optical disk.
2. Description of the Related Art
Generally, an optical pick-up device is used for a computer, a digital video disk (DVD) player and the like to write and read data on or from an optical disk such as a compact disk, a digital video disk, a blue ray disk, and so forth.
In recent years, as a digital device such as a laptop computer, a camcorder and a digital camera has been reduced in weight and size, it has required to miniaturize the size of the data storage reading/writing device.
Particularly, it has been continuously studied to apply the optical disk to a mobile device such as a mobile phone and a personal digital assistant (PDA). In order to apply the optical disk to such a mobile device, it is badly required to miniaturize the size of the optical pick-up device.
The size reduction of the optical pick-up device has been hobbled by an actuator for moving a focus lens to uniformly maintain a distance between the focus lens and the optical disk and tracing a track on the optical disk to write or read data on or from the optical disk.
The optical pick-up device converts a laser beam eradiated from a laser diode into an optical signal and further converts the optical signal into an electrical signal, thereby reading the recorded data.
The actuator of the optical pick-up device is designed to two-dimensionally move in focusing and tracking directions to safely focus the laser beam on the optical disk even when outer impact is applied. In recent years, to provide more precise motion, an actuator that can move in rolling and pitching directions as well as in the focusing and tracking directions has been developed.
FIGS. 1 through 4 shows a prior optical writing/reading device.
A prior optical writing/reading device includes an optical pick-up device 50, an optical pick-up motor 60 for moving the optical pick-up device to a proper position, a lead screw 20 connected to a rotational shaft of the optical pick-up motor 60, a rack gear 30 engaged with the lead screw 20, a guide feeder 10 coupled to the rack gear 30, an optical pick-up moving shaft 21 guiding a reciprocal motion of the guide feeder 10, and a main shaft 22 installed on an opposite side of the optical pick moving shaft 21 to guide the motion of the optical pick-up device.
As the optical pick up motor 60 is operated, the lead screw 20 rotates and the rack gear 30 engaged with the lead screw 20 moves, thereby moving the optical pick-up device 50 to a desired position.
As shown in FIG. 2, the optical pick-up actuator 40 is comprised of a movable part moving a focus lens 49 in the focusing and tracking directions and a stationary part for supporting the movable part and generating magnetic field.
The movable part has a coil cooperating with a permanent magnet 43 provided on the stationary part to locate the focus lens 49 to the desired position.
That is, the stationary part includes the permanent magnet 43 generating magnetic field, a yoke 42 forming a path of the magnetic field, the fixing frame 41 having a main board (not shown), and wire-shaped springs 47 each having a first end 47a fixed on the fixing frame 41 and a second end fixed on the lens holder 44 to support the lens holder 44 and supply electric current to the lens holder 44.
The movable part includes the focus lens 49 focusing a laser beam eradiated from the laser diode on a recording layer of the optical disk, a lens holder 44 holding the focus lens 49, tracking coils 45 installed on both sides of the lens holder 44 to drive the lens holder 44 in the tracking direction, a focusing coil 46 wound around the lens holder 44 to drive the lens holder 44 in the focusing direction, and a spring fixing unit 48 fixing the spring assembly 47 on the lens holder 44.
The movable part should be designed having a desired frequency property by being fixed by a support having a predetermined rigidity and a predetermined damping property. In addition, the movable part should be designed avoiding unnecessary vibration such as rotation or twist to effectively move in the focusing and tracking directions and reduce the optical signal error.
That is, when the movable part drives in the focusing direction, the lens holder 44 should vertically move without rotating in a direction of an X-axis (in the pitching direction shown in FIG. 5). Therefore, as shown in FIG. 3, the spring assembly 47 is comprised of two lower springs and two upper springs stacked on the lower springs that are installed on both sides of the lens holder 44, being extending from the fixing frame 41.
As shown in FIG. 4, in order to eliminate the space limitation in designing the optical pick-up device by reducing a thickness of the actuator, it has been developed that springs 97 may be comprised of one lower spring and one upper spring stacked on the lower spring.
However, in this case, when the optical pick-up device moves in the focusing direction, the lens holder 44 may rotate in the direction of the X-axis, causing the undesired inclination.
Even when the spring assembly 47 is formed as shown in FIG. 3, an elastic coefficient may be varied when the spring is twisted or tensioned during the manufacturing process.